Unit 5 Solar Energy Photo Voltaic
-
Upload
brock33992862 -
Category
Documents
-
view
218 -
download
0
Transcript of Unit 5 Solar Energy Photo Voltaic
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
1/45
Introduction to Alternative EnergiesIntroduction to Alternative EnergiesUnit 5Unit 5 Solar Energy (Photovoltaic)Solar Energy (Photovoltaic)
1
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
2/45
Is There Enough Solar Energy in Ohio? Ohio receives 1.4 megawatt hours per square
meter (MWh/m2) in an average year
Annually residents of Ohio use 4.5 MWh for
electricity and 7.6 MWh for heat
Covered in the previous unit Solar Energy forheat
This unit now covers the systems used for solar
electricity or solar photovoltaic
2
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
3/45
After completing this unit you will
Be able to explain what a photovoltaic
cell is and how it converts sunlight to
electrical energy
Be aware of some of the different typesand variations of photovoltaic cells
Be able to determine the amount ofenergy achieved from a photovoltaic cell
3
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
4/45
What is a
photovoltaic celland how do they
into electric
energy
4
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
5/45
Lets start with
Photovoltaic
Photo = light Voltaic = electricity
Light-electricity or electricity from light
A solar photovoltaic cell produces electricity
from sunlight
5
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
6/45
A simple way to explainphotovoltaics
Is the reverse of an LED
(light emitting diode)
When electricity is applied
to an LED, ig t is emitte Photovoltaics work just
the opposite, when
exposed to light (sunlight) electricity is
produced6
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
7/45
Electricity is the flow ofelectrons electrons are negatively charged particles
Certain materials, called semi-conductors, can
e a apte to re ease e ectrons w en t ey areexposed to light
One of the more common materials is silicon
Silicon is the main material in 98% of photovoltaic
cells made today
http://www.co-operativebank.co.uk/
7
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
8/45
The main parts of a photovoltaic cell aretwo layers of a modified (doped) semi-
conductive material
The N-Layeris blended with
phosphorous, making it rich in electrons
The P-Layeris blended with boron,
making it electron-poor leaving
positively-chargedholes whereelectrons can fit
8
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
9/45
At the junction of the N and P-layers is anelectrically neutral barrier
This barrier makes it difficult for the extra
electrons of the N-layer to jump over to fill the
holes in the P-layer
On t e outsi e o t e N an P- ayers isconductive material, which is connected
(wired) to an electrical load
This creates a closed circuit and a current pathfor the electrons to flow from the N-layer to
the P-layer9
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
10/45
A photovoltaic cell
Protective glass
Anti-reflective coat
Photons from the sun
P-type silicon
Conductive backing
Conductive mesh
N/P junction
N-type siliconLoad
-- -- --
-- -- --
--
--
10
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
11/45
The conductive material on the N-layer side isa mesh allowing sunlight to pass through
When energy is added to a semi-conductive
material, such as silicone, it can cause
electrons to break free from their atoms
In the case of a photovoltaic cell, energy
from the sun hits the electron-rich N-layer in the form of light photons and
causes electrons to break free
11
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
12/45
If they are close enough to the P-layer, theseelectrons can jump across the electrical field
and fill the P-layer's holes
The resulting electrical imbalance encourages
these electrons to flow back to the N-layer
,
The greater the intensity of the light,
the greater the flow of electricity
12
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
13/45
Theoretical Efficiency
100% efficiency is
achieved when exposedto monochromic light
,
typically not the case
Typically they are
exposed to the fullspectrum of light (right
side of figure)
13
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
14/45
When exposed to the full spectrum, there aretwo mechanisms that will limit efficiency
Photons that do not have enough energy to create
the electron-holes and just pass through creatingonly heat
Photons that have too much ener creatin
electron-holes too fast and are quickly dissipatedbefore generating any electric energy
The efficiency is then the ratio of the load
power to the input power of the radiation
14
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
15/45
What are some
different types orvariations of
15
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
16/45
Spectrally Selective Beam Splitting
As noted, depending on the material, only a
portion of the solar spectrum is used
Therefore, when manufacturing the
, -
spectrum must be split into appropriate
sections with corresponding frequencies
This can be accomplished in several differentways including cascaded cells, filtered cells,
and holographic concentrators
16
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
17/45
Cascaded cells are basically two photodiodeswith different band-gaps superimposed
As the solar energy passes through the top
photodiode, the relevant band-gap is used
The remaining spectrum passes through to
t e next p oto io e w ere a i erentband-gap is used
Conceptually, very simplified
a solar spectrum sieve
17
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
18/45
Filtered cells work in one of two differentmethods
Absorption, where sunlight passes through a
particular substance such as cobalt sulfate
which absorbs certain bands of the spectrum
Interference, where different materials are
used to refract different parts of the spectrum
allowing only the specific band of thespectrum needed
18
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
19/45
Holographic concentrators are probably themost attractive of the different devises
These devises take the sunlight and split it
into separate bands and refocuses the
specific sections of the spectrum
T e p oto io es can t en e mounte insuch a manner that the various photodiode
materials can align with the appropriate
section of the spectrum
19
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
20/45
Thermo-photovoltaic Cells
Another method of increasing
the efficiency of photovoltaicconverters is to recirculate
for electric generation for
heat
This can be accomplishedseveral different ways
20
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
21/45
One method includes placing the photodiodebetween a thermal radiator and a mirror
As the unused energy passes through the
photodiode, it is reflected back through to thethermal radiator
photodiode and a thermal radiator
As the energy passes through the selective
mirror, only the useable band-gap passes
through to the photodiode and the remaining is
reflected back to the thermal radiator
21
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
22/45
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
23/45
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
24/45
The thinness of the cells When the cells are excessively thin, they fail to
react with the available light
Material for the cells is very expensive and theremust be compromise between cost and thickness
And the lifetime of the minority carriers, as
some of the electron holes are created too far
from the potential barrier to survive thelength of time needed to reach it by diffusion
24
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
25/45
How do you
determine the
amount of energy
photovoltaic cell
25
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
26/45
Economics The obvious benefit of photovoltaic
converters is that the energy (solar) isbasically free
,
available at certain times of the day and
some days may be overcast
The supply is not constant, therefore,the cost associated with these systems is
for the converting and storage of energy
26
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
27/45
There are many different ways to look at thecost of photovoltaic converters, which have
been coming down in price over the last few
years due to improvements in technology
Related to cost is efficiency ranging from 5%
the system which affects the cost of the
system
Beyond the cost of the system, there arecosts associated with installation and
maintenance27
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
28/45
This cost is then compared to the benefit orthe energy obtained
Since the solar energy is not constant, there
are times when there is excess energy
produced and times when no energy is
Depending on the type of system and local
utilities the excess power can be sold back to
local utility companies or used to offset utilitycostsThis type of system would be referred
to as a utility-tie system28
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
29/45
With a utility-tie systemthere is a utility service inverter tied to the system
used to match the frequency and phase of generated
solar energy to the grid
http://internationalenergysolutions.com/index-2.html 29
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
30/45
For areas that cannot be tied to a local utility,a system referred to as an off-gridsystem
could be used which incorporates batteries
Hybrids of these two
systems integrated
buildings, building-
integrated
photovoltaic(BIPV)systems are becoming
very popular
30
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
31/45
These systems are typically placed on or as theroof of a building creating a large surface area
This system is more appealing to single story
buildings versus a several story complex and,therefore, is more suited to residential
One thing that must be considered is the peak
solar energy available which is dependent on
your location
31
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
32/45
Different materials and techniques for buildingthe solar cells also have relevance to the cost
and return, three of which are
1. Silicon
2. Amorphous thin films
3. And organic polymers which are still in theearly stages of development
* The organic polymers may be the best solution
showing promise to be light weight, flexible andrelatively low in cost leading to more applications
and thus better economics
32
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
33/45
Energy potentialTo roughly determine the amount of energy
from a photovoltaic system is relatively simple
You will need the ollowin in ormation
a. As with solar collectors, you need the solarpotential or energy production factor for your
area in kilowatt-hours per kilowatt-year
(kWh/kW-year)b. And the size of the system in kilowatts (kW)
33
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
34/45
The map below, from the U.S. Department ofEnergy-Energy Efficiency and Renewable
Energys web site,
shows the energypotentialfor
different re ions
of the Unitedstates in
kilowatt-hours
per kilowatt-year(kWh/kW-year)
http://apps1.eere.energy.gov/consumer/your_ho
me/electricity/index.cfm/mytopic=10860
34
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
35/45
Looking at the Columbus, Ohio area, asin the previous section, you see the
energy potential is around 1500
(kWh/kW-year)
35
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
36/45
A photovoltaic system typically ranges in sizefrom 1 to 5 kW
The table below,from the California Energy Commission's Buying a
Photovoltaic Solar Electric System, Consumers Guide, 2003 edition, showsvarious PV capacity ratings with the related roof area needed
Note: the (5) solar collectors used in the previous
section used a total roof area of 159 ft236
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
37/45
To roughly determine the availablepowerperyear (kWh/yr) of a photovoltaic system, you
simply multiply the energy production factor by
the system size
kWh/yr= energy prod. x system size
Where :
energy production factor is (kWh/kW-yr)
system size is (kW)
37
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
38/45
Using the example from the previous unitLiving in Columbus, Ohio, determine the
annual energy potential for a 2 kW
photovoltaic system
(kWh/yr) = energy prod. x system size= 1500x 2
= 3000 kWh/yr
Note: the (5) solar collectors used in the previoussection produced 7884 kWh/yr
38
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
39/45
Comparing a similar sized roof area, 160 ft2
, thehighest efficiency (16%) would be required
and from this you can assume cost to the high side,
$20,000 for a 2 kWh system, which produces less
than half the kWh/yr of the solar collectors
39
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
40/45
How about an
interesting
concept
40
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
41/45
Solar-Power Satellite As we have learned, the idea of using
photovoltaic converters to generateelectricity is definitely a possibility
utt ey are epen ent on t e a ty o agiven area to collect the solar energy
Therefore, areas that do not receive large
amounts of continuous sunlight will notfind this technology as appealing as others
41
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
42/45
The concept of a solar power satellite couldeliminate the concern for continuous sunlight
by placing the solar collectors into space
orbiting to receive constant solar energy
42
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
43/45
As the orbiting solar collector absorbs theenergy, it can convert it and then transmit it
to collectors on Earth
43
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
44/45
ORWhat if the same concept was
used on some kind of vesselthat traveled the Earthssurface so as to remain inconstant sun g t
This vessel could then convert thesolar energy to electricity and
transmit it via satellites or othermeans to various locations aroundthe rest of the Earth
44
-
8/9/2019 Unit 5 Solar Energy Photo Voltaic
45/45
Da Rosa, A. V. (2005). Fundamentals of Renewable Energy Processes. Burlington, MA,
USA: Elsevier Inc.
http://sales.hamamatsu.com/assets/html/ssd/si-photodiode/index.htm
Work Cited
45